AB1681 ARE PR3 ANTIBODY TITERS REALLY IMPORTANT FOR ROUTINE CLINICAL PRACTICE?. STUDY FROM A SINGLE UNIVERSITY HOSPITAL
Authors: V. Calvo-Río, S. Al Fazazi, M. Renuncio-García, M. Rodriguez Vidriales, C. Escagedo Cagigas, J. Irure-Ventura, L. Martín-Penagos, A. Herrero-Morant, M. Lopez-Hoyos, R. Blanco
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Anti-proteinase 3 are one of the main ANCA subtypes. There are contradictory studies on the relation between ANCA levels and the severity of the disease and its prognosis [1]. <h3>Objectives</h3> In patients with positive anti-PR3 antibodies from a university hospital we assess: <b>a</b>) associated diseases, <b>b</b>) specificity in diagnosing AAV and, <b>c</b>) determine if there is a cut-off point that allows to correlate the levels of anti-PR3 antibodies with the severity and prognosis of AAV. <h3>Methods</h3> Observational study of patients with positive anti-PR3 from a University Hospital, from 2003 to 2022. ANCA was determined by chemiluminescence. The specificity of anti-PR3 for AAV diagnosis, predictive value of severity and prognosis were determined with Receiver Operating Characteristic (ROC) curves. At diagnosis, AAV with renal disease (hematuria and/or proteinuria) and lung involvement (hemoptysis, asthma and/or respiratory failure) were considered severe. During follow-up, the prognosis was considered worse if the patient needed dialysis, a transplant, or died. <h3>Results</h3> We study 54 patients with positive PR3. Most of them (81.5%) had an underlying AAV being the most frequent GPA (61.1%). The non vasculitic disease more frequent was Ulcerative colitis (11.1%). <b>Table</b> 1 summarizes the prevalence of these antibodies in different diseases. The frequencies are equivalent to those previously described and it is noteworthy the presence of anti-PR3 in drug-induced vasculitis, mainly by cocaine. Anti-PR3 antibodies for a diagnosis of vasculitis (n=44), an area under the curve (AUC) was calculated (AUC=0.7318), and a cut-off point of 20.5 IU/ml was determined <b>(Figure 1).</b> Significant differences in anti-PR3 levels were observed between those patients with renal or pulmonary dysfunction (n=30) and those without them (n=24) (p=0.0048), and a cut-off threshold of 41.5 IU/ml was established. Finally, after examining the illness's prognosis an AUC= 0.5643 was obtained, being no significant differences between those patients who had a worse disease progression (n=14) and those who did not (n=40) (p=0.4847). <h3>Conclusion</h3> The presence of anti-PR3 is mainly associated with AAV, although in up to a fifth of cases it can be associated with other diseases. Anti-PR3 antibodies levels, at the moment of AAV diagnosis, correlates with disease diagnosis (specificity) and with severity but not with disease outcome. <h3>References</h3> [1]Walker BS, et al. Autoimmun Rev. 2022 Jun;21(6):103100. [2]Kitching AR, et al. Nat Rev Dis Primers. 2020 Aug 27;6(1):71 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Vanesa Calvo-Río Speakers bureau: AbbVie, Lilly, MSD, UCB Pharma, Grunenthal and Celgene., Salma Al Fazazi: None declared, Mónica Renuncio-García: None declared, Maria Rodriguez Vidriales: None declared, Clara Escagedo Cagigas: None declared, Juan Irure-Ventura: None declared, Luis Martín-Penagos: None declared, Alba Herrero-Morant: None declared, Marcos Lopez-Hoyos: None declared, Ricardo Blanco Speakers bureau: Abbvie, Pfizer, Roche, Bristol-Myers, Janssen, Lilly and MSD, Grant/research support from: Abbvie, MSD and Roche.